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IC 


9023 



Bureau of Mines Information Circular/1985 



Bulk Mineralogy and Geochemistry 
of Selected Alaskan Chromian 
Spinel Samples 



By William S. Roberts 




UNITED STATES DEPARTMENT OF THE INTERIOR 



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4f/NES 75TH A^ 



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nformation Circular) 9023 



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Bulk Mineralogy and Geochemistry 
of Selected Alaskan Chromian 
Spinel Samples 



By William S. Roberts 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



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Library of Congress Cataloging in Publication Data: 



Roberts, William S 

Bulk mineralogy and geochemistry of selected Alaskan chromian 
spinel samples. 

(Information circular / United States Department of the Interior, 
Bureau of Mines ; 9023). 

Bibliography: p. 9. 

Supt. of Docs, no.: I 28.27:9023. 

1. Spinel— Alaska— Composition. 2. Chromite — Alaska— Composi- 
tion. I. Title. II. Series: Information circular (United States. Bu- 
reau of Mines) ; 9023. 



TN295.U4 TQE39LS681 622s T549\ 5261 84-600362 



CONTENTS 



Page 



Abstract 1 

Introduction 2 

^- Acknowledgments 2 

Samples 2 

<V) Procedures 2 

\ Nomenclature and mineralogy 4 

\ Results 5 

X-ray diffraction 5 

X-ray fluorescence 5 

\i Conclusions 8 

References 9 

Appendix A. — Analytical results 10 

Appendix B. — Number of cations per 32 oxygens 12 

Appendix C. — Mineral terms and sample key 13 

ILLUSTRATIONS 

1. Locations of ultramafic rocks hosting chromian spinel occurrences charac- 
terized in this report 3 

2 . Schematic diagram of sample preparation procedures 4 

3. Nomenclature of chromium-bearing spinels based on molecular proportion plot 
of divalent and trivalent cations 4 

4. Unit cell dimensions of chromian spinel based on (113) reflection 6 

5. Molecular proportion plot of purified chromian spinel samples 6 

6 . Trace Ni versus Cr 7 

7. Trace Zn versus Cr 7 

8 . Trace Ti versus Cr 8 

TABLES 

1 . Range of oxide concentrations in chromian spinel samples 7 

2. Statistical comparison of oxides and lattice data for the interior Alaska 
and Chugach group of samples 7 








UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 


A 


angstrom wt % weight percent 


ppm 


part per million 



BULK MINERALOGY AND GEOCHEMISTRY OF SELECTED ALASKAN 
CHROMIAN SPINEL SAMPLES 

By William S. Roberts 1 



ABSTRACT 

As part of the Bureau of Mines critical and strategic minerals pro- 
gram in Alaska, 34 high-purity chromian spinel samples were analyzed 
for trace and major element geochemistry and mineralogy. The samples 
were analyzed by X-ray diffraction, X-ray fluorescence, and chemical 
techniques. 

Systematic differences in chemistry are evident when samples collected 
from the Chugach Mountains and their related extension are compared with 
chromian spinel samples collected from interior Alaska. Compared with 
the Chugach samples, the interior Alaska samples have higher average 
amounts of AI2O3, Fe203, TiC>2, and NiO, have lower average amounts of 
FeO and Cr 2 03, and exhibit greater dispersion in values. 

Considerable mineralogical variability of chromian spinel exists be- 
tween and within individual Alaskan chromite-bearing ultramafic com- 
plexes. Of 34 samples analyzed, 25 samples are magnesiochromite, 5 
are chromite, 3 are spinel, and 1 is hercynite. As a group the inte- 
rior Alaska samples have a smaller average unit cell dimension than the 
Chugach group of samples. 

The chemical and mineralogical differences between the two groups of 
samples can be attributed to different genetic histories and may have 
implications for locating chromian spinel deposits amenable to standard 
benef iciating techniques. 



Physical scientist, Alaska Field Operations Center, Bureau of Mines, Juneau, AK. 



INTRODUCTION 



This report summarizes mineralogical 
and geochemical work done on samples col- 
lected during field investigations of 
Alaskan chromite occurrences. Field work 
assessing chromite deposits, as part of a 
critical and strategic minerals program, 
began in 1981 by the Bureau of Mines 
Alaska Field Operation Center (AFOC), and 
several deposits have recently been de- 
scribed (_6-_7> 11) .2 Benef iciation stud- 
ies of chromian spinel samples have been 
done by the Bureau's Albany Research Cen- 
ter (ALRC) (3-A)- 

The purpose of this study is to charac- 
terize and compare the geochemical deter- 
minations for 34 purified chromian spinel 
samples. The samples, plus 18 other 
chromian spinel samples , were analyzed by 



X-ray diffraction. Chromite mineralogy 
is sufficiently complex to require a com- 
bination of X-ray diffraction, X-ray 
fluorescence, and chemical analyses for 
characterization. 

Previous studies have focused on the 
description of chromian spinel occur- 
rences and standard benef iciation tests 
of bulk samples. Mineralogical deter- 
minations have generally been restricted 
to the identification of gangue and trace 
minerals associated with chromian spinel. 
This report provides information on the 
mineralogy of Alaskan chromian spinel 
samples and reports trace and major oxide 
chemical signatures of samples collected 
statewide. 



ACKNOWLEDGMENTS 



K. Broadhead, metallurgical engi- metallurgist, Albany 
neer, Reno Research Center, provided provided splits of 
the FeO determinations, and D. Dahlin, samples. 



Research Center, 
chromian spinel 



SAMPLES 



Fifty-two samples were collected by Bu- 
reau personnel. The samples represent 
splits taken from grab or bulk samples 
that were high-graded in the field for 
mineralogical and benef iciation tests. 
The results of this study represent 
reconnaissance-type information since a 
few samples from each occurrence do not 
constitute a thorough characterization 
for any single deposit, area, or region. 

The samples were obtained from widely 
scattered ultramafic occurrences across 



the State; however, all chromian spinel 
occurrences in Alaska are not represented 
in this report (fig. 1). For comparative 
purposes the samples are lumped into two 
logical groups that are based on geo- 
graphic location or extension of geo- 
graphic or geologic features. The two 
groups include the interior Alaska and 
Chugach groups. General localities and 
grouping of the samples are indicated in 
appendix C. 



PROCEDURES 



The procedures used for this study are 
not standard concentration techniques. 
High-purity chromian spinel samples are 
required for mineralogical characteriza- 
tion using molecular proportion plots, so 
modified laboratory techniques were used. 

^Underlined numbers in parentheses re- 
fer to items in the list of references 
preceding the appendixes. 



Two different sources for samples 
resulted in slight variations in the 
concentration procedures. Samples ar- 
chived at AFOC were prepared in the man- 
ner outlined in figure 2. Samples re- 
ceived from ALRC were table concentrates 
of minus 28-plus 65-mesh sized fraction, 
so crushing and hand picking were not 
required. 



Borrow 




FIGURE 1. - Locations of ultramafic rocks hosting chromian spinel occurrences characterized in this 
report. A, Avan Hills; 5, Caribou Mountain, Kanuti River; C, Yuki River; D, Mount Hurst; E, Tonsina- 
Bernard, Sheep Hill; F, Wolverine Complex, Eklutna; G, Claim Point, Red Mountain; H, Miners Bay, Grant 
Lagoon, Halibut Bay; /, Red Bluff Bay. 



The samples were run through a labora- 
tory model isodynamic magnetic separator 
to remove all magnetite, and a hydroflu- 
oric acid (HF) bath effectively removed 
unwanted silicate minerals. The HF bath 
altered the magnesium silicates to chon- 
drodite, a relatively low density, frag- 
ile f luorohydroxide which could be washed 
out by agitation and wet screening. 
There is no evidence the HF bath altered 
the chemistry or mineralogy of the chro- 
mian spinels. 

High-purity chromian spinel concen- 
trates free of magnetite and silicates 
were analyzed by energy-dispersive X-ray 



fluorescence spectrometry (XRF), with the 
exception of FeO, which was analyzed 
by wet chemical methods. Ferric oxide 
(Fe 2 03) was calculated from total Fe. 

The analytical precision is less than a 
few percent relative error, while errors 
in accuracy may range as high as ±20% in 
the case of Mg or trace elements because 
of low counting rates. Comparison of Fe 
and Cr determinations by ALRC and AFOC 
during this study generally indicates a 
relative error in accuracy of ±5% to 10% 
or less. National Bureau of Standards 
NBS103A was the primary reference stan- 
dard used in the XRF determinations. 



Chromite sample 



Crush to minus 1/4 inch 



Hand sort 



Grind 



Screen (minus 20 plus 100 mesh) 



Magnetic separation 



HF acid bath 



Wash, agitate, wet-screen (minus 100 mesh) 



Regrind to minus 300 mesh (nominal) 



X-ray fluorescence and chemical analysis 



Diffraction analysis 

FIGURE 2. - Schematic diagram of sample preparation 
procedures. Samples received from Albany were con- 
centrated using tabing methods, and splits consisted of 
minus 28- plus 65-mesh fractions. These samples were 
treated beginning with the magnetic separator. 



After analysis by XRF the samples were 
analyzed by X-ray diffraction using 
two modes: a scanning speed of 1/4° 
two-theta per minute from 31° to 37° 
two-theta, and a scanning speed of 2° 



(8 0831) , 

MgAljOa ' 





(8.119) 
FeAljO, 



Cr /Cr .Al 





1 

I (Pleonaste) 




- 


Spinel 


Hercynite 


i 




- 


i 

i (Mitchellite) 

1 

l 
l 


(Piconie) i 


- 


Mognesiochromite 


Chromite 




1 l 


i ' 




MgCr 2 4 


0.2 


4 6 


(8.333) 




Fe 2 */Fe ! * + Mg** 



(8 360) 



FIGURE 3. - Nomenclature of chromium-bearing spi- 
nels based on molecular proportion plot of divalent and 
trivalent cations. Note: Changes along horizontal axis 
reflect different proportions of divalent cations (Fe, 
Mg), and changes on the vertical axis represent differ- 
ent proportions of trivalent cations (Cr, Al). Unit cell 
dimensions, in angstroms, are indicated in parentheses 
and are for end member minerals only. 



two-theta per minute from 2 to 62° two- 
theta. Measured precision of d-spacings 
in the former mode is ±0.0005 A. An in- 
ternal standard (NaCl) was used to stan- 
dardize the d-spacing measurements using 
a full-width-half -maximum technique of 
marking peak centroids. 

The (113) d-spacing, the strongest spi- 
nel reflection, was used to calculate 
unit cell dimensions. Since multiple re- 
flections from different crystallographic 
planes were not used to calculate the 
unit cell dimensions, the values reported 
must be considered provisional. 



NOMENCLATURE AND MINERALOGY 



Mineral nomenclature is adapted from 
Palache ( 10 ) and conforms to terminology 
used by the Joint Committee Powder 
Diffraction Society ( 1) . Chromite from 
podiform and stratiform ultramafics is 



mineralogically part of the spinel group, 
which consists of the magnetite, spi- 
nel, and chromite series. Spinel-group 
minerals may be represented by the gener- 
al formula AB 2 X 4 , which may be expressed 



as R 2+ R 3+ (13) . Extensive ionic sub- 
stitution of divalent cations (Fe, Mg, 
and Ti) and trivalent cations (Cr, Al, 
Fe , and Mn) makes characterization by X- 
ray diffraction difficult since crystal 
lattice dimensions are variably affected 
by substitution at the octahedral and 
tetrahedral positions. Although there 
are natural limits on ionic substitution, 
characterization is best achieved by com- 
bining X-ray diffraction and quantitative 
chemistry. 

Low-titanium chromium-bearing spinels 
consist of six idealized end members: 
chromite (FeCr 2 4 ), magnesiochromite 



(MgCr 2 04), hercynite (FeAl 2 C>4), spinel 
(MgAl 2 04), magnesioferrite (MgFe 2 4 ), and 
magnetite (Fe304) ( 9) . A multi component 
prism described by Haggerty (8) best 
characterizes chromium spinels, but for 
this study only the base of the prism 
is used. Figure 3 outlines, on a molecu- 
lar proportion plot, the fields repre- 
sented by four of the end-member minerals 
listed above. Magnesioferrite and mag- 
netite are not represented on the plot, 
although there is an appreciable ferrian 
(Fe+ 3 ) component represented by the 
analyses. 



RESULTS 



The results of the chromian spinel 
chemical analyses are presented after a 
brief discussion of X-ray diffraction re- 
sults. Diffraction data for 52 samples 
are listed in appendix A, along with 
chemical results for 34 samples. Molecu- 
lar proportions of the principal spinel 
cations are listed in appendix B, and 
mineral terms and general localities are 
tabulated in appendix C. 

X-RAY DIFFRACTION 

High-resolution X-ray diffraction in- 
dicates that average d-spacings of the 
(113) reflection vary from 2.4835 to 
2.5260 A. These measurements indicate 
unit cell dimensions of 8.237 to 8.378, 
respectively. Figure 4 represents a plot 
of calculated cell dimensions with sum- 
mary envelopes of the Chugach and inte- 
rior Alaska groups of samples. There is 
a clear difference in average cell dimen- 
sions, with the Chugach group averaging 
8.312 A and the interior Alaska group 
averaging 8.279 A. The disparity in unit 
cell dimensions is apparently due to a 
difference in average amounts of Al, Mg, 
Fe, and Cr. 



Eleven samples have multiple (113) re- 
flections ("doublet"), indicating more 
than one spinel mineral is present. Nine 
of the 11 samples with doublets are from 
the Chugach group of samples. Dahlin (3) 
and Bliss (2) describe zoned chromian 
spinel minerals , which are the probable 
cause for the doublets. 

X-RAY FLUORESCENCE 

Plots comparing molecular proportions 
of Fe 2+ /Fe 2+ + Mg 2+ and Cr 3+ /Cr 3+ + Al 3+ 
concentrations are presented in figure 5. 
The plots define R 2+ and R 3+ cation 
proportions and the mineralogy of the 
high-purity bulk chromian spinel splits. 
Fe +3 is not represented on the plot even 
though the chemical analyses indicate an 
appreciable ferrian component. 

Mineral terms for 34 samples are based 
mainly on molecular proportions. Analy- 
sis by X-ray diffraction was used to 
check purity of the samples and to con- 
firm the presence of a spinel. A total 
of 25 samples are characterized as mag- 
nesiochromite, 5 are chromite, 3 are spi- 
nel, and 1 is hercynite. 



® 



/ . 


i -- — 




1 : 


* 


\ 


1 . 


• 


• 1 



® 




./ 

/ Chugacti G 



-Interior Alaska Group 



Eklutna, 
Wolverine 



Red 

Mountoir 



LOCALITY 



FIGURE 4. - Unit cell dimensions of chromian spinel 
based on (113) reflection. Note: Envelopes are used 
to diagrammatically illustrate differences between the 
interior Alaska and Chugach groups of samples. The 
range of cell dimensions shows the variation in chro- 
mian spinel compositions within a related area or 
complex. 




Avon 

Kanuti, Caribou 
Yuki River 
Mount Hurst 
Eklutno, Wolverine 



Red Mountain, 
Claim Point 

Kodiak 
Tonsino 
Southeast 



FIGURE 5. - Molecular proportion plot of purified 
chromian spinel samples. Note: Refer to figu,re 3 
for mineral nomenclature. 



The concentrations of major oxides in 
the chromian spinel samples exhibit con- 
siderable variability (table 1). This 
variability exists not only between 
regions , but between samples taken with- 
in the same ultramafic complex. This 
emphasizes the importance of understand- 
ing the chemistry and mineralogy of 
chromian spinel occurrences since the 



benef iciating procedures and market de- 
pend heavily on ore chemistry. 

Systematic chemical and unit cell dif- 
ferences exist between the Chugach and 
interior Alaska samples when the groups, 
rather than specific samples, are com- 
pared. Compared with the Chugach group 
of samples , the interior Alaska group 



TABLE 1. - Range of oxide concentrations in chromian spinel samples, weight percent 



Oxide 1 


Minimum value 


Maximum value 


Mean value 


Al oO t. 


4.5 
7.0 
25.8 

4.2 


17.7 
26.7 
59.8 
15.6 
22.0 


11.4 
13.9 


Cr oO 7 


49.5 


Fe oO * 


8.2 




14.5 



1 0xide 
cally by 
from tot 



s based on X-ray fluorescence analyses except FeO which was determined chemi- 
the Bureau of Mines, Reno Research Center. The Fe 2 03 values were calculated 
al iron. 



samples have higher average amounts of 
A1 2 3 , Fe 2 3 , Ti0 2 , and NiO and exhibit 
greater dispersion in values (table 2). 
Figures 6, 7, and 8 graphically summarize 
the differences between the two groups 



when Ni , Zn, and Ti concentrations are 
compared to Cr content. The significance 
of the chemical differences between the 
groups can be attributed to different 
genetic histories. 



TABLE 2. - Statistical comparison of oxides and lattice data for the interior 
Alaska and Chugach group of samples 



Statistical parameter 



Interior Alaska group 



N 



Mean wt % 



SD, 2 wt % 



N 



Chugach group 



Mean wt % 



SD, 2 wt % 



MgO . . , 
A1 2 3< 
FeO... 
Fe 2 3< 
Cr 2 3 . 
Si0 2 .. 
P 2 5 .. 
Ti0 2 .< 
NiO... 



ZnO , 

d-spacing, 
Unit cell, 



17 
17 
17 
17 
17 
17 
17 
17 
17 
17 
27 
27 



11.2 

17.4 

12.7 

9.5 

46.4 

0.27 

0.12 

0.50 

0.10 

0.11 

2.4965 

8.279 



2.1 

8.9 

4.3 

4.1 

11.6 

0.19 

0.04 

0.22 

0.04 

0.10 

0.0075 

0.024 



17 
17 
22 
17 
17 
17 
17 
17 
17 
17 
27 
27 



11.5 

10.4 

15.8 

6.9 

52.5 

0.27 

0.11 

0.30 

0.06 

0.09 

2.5060 

8.312 



3.9 

3.8 

4.0 

3.5 

6.1 

0.21 

0.04 

0.15 

0.03 

0.09 

0.0081 

0.027 



In = 



N = number of observations. 2 SD = standard deviation. 



tn 


^_^^ 










40 




o\ 




.1 


nterior Alaska Group 




i --" * ffi A \. 




\ 


4 






\ (o #\ 




• 




N 




35 


\ X D \ V 

X \ D 


O 








\ 

\ 

\ 












o\ 


30 


\ \ * 




o 

• 






\ 
\ 
\ 


25 


Chugach Group' \ * 
\ 
\ 








\ 
\ 
\ 


20 


\ 
\ • 








oj 




\ ___ 




o 




y 














15 













600 800 

Ni, ppm 



Avon 

Kanuti, Coribou 
Yuki River 
Mount Hurst 
Eklutno, Wolverine 



,000 1,200 

Red Mountain, 
Claim Point 

Kodiak 
Tonsino 
Southeast 



1,400 1,600 



FIGURE 6- - Trace Ni versus Cr. Note: Envelopes are 
usedto diagrammatical ly illustrate differences between 
the interior Alaska and Chugach groups of samples. 



4b 
40 


„ 

l \ • \ \ 


^hugoch Group 




35 








X °° 








v\ 


_3 o\ 




.10 


\ \-Q - — 

\o « 








\ 






\ 


\ 






\ . 


i 


n 


2b 


\ 








\ 
\ 


. ^Interior 


Alaska Group 


20 


\ 

\ 








v9_ 


^ 




15 











500 


1,000 
Zn, ppm 

KEY 




1,500 


■ 


Avon 




A 


Red Mounto 
Claim Point 


o 


Kanuti, Caribou 




* 


Kadiok 





Yuki River 




D 


Tonsino 


9 




Mount Hurst 
Eklutno, Wolver 




X 


Southeast 



FIGURE 7. - Trace Zn versus Cr. Note: Envelopes are 
usedto diagrammatica I ly illustrate differences between 
the interior Alaska and Chugach groups of samples. 



45 



40 - 



35 



_ 30 



20 



15 - 



10 



-(*"" 




— — 


^i\ 


aV a ^> 




/^a® ® 




v^ ^Interior Alaska Group 




\x X D \ v j 


/ ° 


\ 








- 


/ ^ 


# 


o \ 




Chugach Group . 




\ 
\ 




\ 




a« \ 




\ 


ffi 


\ 




\ 




N 






\ 


\ 








. N 

- — — — ____ o^ 








i i i i 



1,000 





2,000 3,000 




4,000 5, 






Ti 


, PPm 






• 


Avan 




KEY 


A 


Red Mountain, 
Claim Point 


o 


Kanuti, Caribou 






* 


Kodiak 


«* 


Yuki River 






D 


Tonsina 


© 


Mount Hurst 






X 


Southeast 



5,000 



6,000 



7,000 



Eklutna, Wolverine 

FIGURE 8. - Trace Ti versus Cr. Note: Envelopes are used to diagrammatically illustrate differ- 
ences between the interior Alaska and Chugach groups of samples. 

CONCLUSIONS 



The following conclusions are based on 
X-ray diffraction, X-ray fluorescence, 
and chemical analyses of 34 high-purity 
chromian spinel samples: 

1. Samples that are grouped by region 
or geologic extension have systematic 
chemical differences when average values 
are compared. The interior Alaska group 
of samples, when compared to the Chugach 
group of samples , have higher average 
amounts of AI2O3, Fe 2 03, Ti0 2 , and NiO, 
exhibit greater dispersion in values, 
have lower average amounts of FeO and 
Cr 2 03, and have similar average MgO 
concentrations . 

2. Considerable mineralogical varia- 
bility exists between and within indi- 
vidual Alaskan chromian spinel-bearing 



ultramafic complexes. Of 34 chromian 
spinel samples analyzed, 25 consist of 
ferroan or aluminian magnesiochromite, 5 
are aluminian or magnesian chromite, 3 
are chromian spinel, and 1 is chromian 
hercynite. The Chugach sample group has 
a larger average unit cell dimension when 
compared to the interior Alaska group of 
samples and has a higher incidence of 
doublet (113) diffraction reflections, 
indicating the presence of more than one 
spinel phase. 

3. The chemical and mineralogical dif- 
ferences between the groups may be a sig- 
nificant factor in the location of chro- 
mian spinel deposits amenable to standard 
beneficiating techniques. 



REFERENCES 



1. Berry, L. G. (ed.). Selected Pow- 
der Diffraction Data for Minerals. Joint 
Committee on Powder Diffraction Stan- 
dards, Swarthmore, PA, 1974, 833 pp. 



Caribou Mountain and Lower Kanuti River 
Areas, Central Alaska. Part 1. Recon- 
naissance Investigations. BuMines IC 
8915, 1983, 27 pp. 



2. Bliss, N. W. , and W. H. MacLean. 
The Paragenesis of Zoned Chromite From 
Central Manitoba. Geochim. et Cosmochim. 
Acta, v. 39, 1975, pp. 973-990. 

3. Dahlin, D. C. , L. L. Brown, and 
J. J. Kinney. Podiform Chromite Occur- 
rences in the Caribou Mountain and Lower 
Kanuti River Areas, Central Alaska. 
Part 2: Beneficiation. BuMines IC 8916, 
1983, 15 pp. 

4. Dahlin, D. C. , D. E. Kirby, and 
L. L. Brown. Low-Grade Chromite Deposits 
Along the Border Ranges Fault , Southern 
Alaska. 2. Beneficiation. BuMines IC 
8991, 1984. 

5. Deer, W. A., R. A. Howie, and J. 
Zussman. An Introduction to the Rock- 
Forming Minerals. Longman Group Limited, 
1966, pp. 424-433. 

6. Foley, J. Y. , and J. C. Barker. 
Low-Grade Chromite Deposits Along the 
Border Ranges Fault, Southern Alaska. 
1. Field Investigations and Descriptions 
of Chromite Deposits. BuMines IC 8990, 
1984. 

7. Foley, J. Y. , and M. M. McDermott. 
Podiform Chromite Occurrences in the 



8. Haggerty, S. E. Opaque Mineral 
Oxides in Terrestrial Igneous Rocks. 
Sec. in Oxide Minerals. Mineralogical 
Society of America Short Course Notes, 
v. 3, Nov. 1976, pp. 101-150. 

9. MacGregor, I. D. , and C. H. Smith. 
The Use of Chrome Spinels in Petrographic 
Studies of Ultramafic Intrusions. Can. 
Mineral., 1962, pp. 403-412. 

10. Palache, C. , H. Berman, and C. 
Frondel. The System of Mineralogy of J. 
D. Dana and E. S. Dana. Wiley, v. 1, 7th 
ed. , 1944, pp. 687-712. 

11. Roberts, W. S. Economic Potential 
for Chromium, Platinum, and Palladium in 
the Mount Hurst Ultramafics, West-Central 
Area, Alaska. BuMines OFR 22-84, 1984, 
52 pp. 

12. Stevens, R. E. Composition of 
Some Chromites of the Western Hemisphere. 
Am. Mineral., v. 29, Nos. 1-2, 1944, 
pp. 1-34. 

13. Thayer, T. P. Principal Features 
and Origin of Podiform Chromite Deposits, 
and Some Observations on the Guleman- 
Soridag District, Turkey. Econ. Geol. , 
v. 59, 1964, pp. 1497-1524. 



10 



APPENDIX A. —ANALYTICAL RESULTS 



Sample No 


1 


2 


3 


4 


5 


6 


7 


8 


9 


10 


Analysis, wt %: 
MgO 


NA 
NA 
Na 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
2.5010 
8.295 


9.8 
11.5 
15.0 

2.5 
58.7 
0.06 
0.15 
0.56 
0.09 
0.05 
2.5015 
8.297 


9.3 

26.7 

15.0 

7.5 

38.3 

0.63 

0.08 

0.76 

0.12 

0.08 

2.4845 

8.240 


NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
2.4970 
8.282 


NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
2.5025 
8.300 


NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
2.4970 
8.282 


NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
2.4985 
8.287 


8.1 
29.8 
18.0 
14.3 
27.4 
0.24 
0.10 
0.89 
0.09 
0.14 
2.4870 
8.248 


NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
2.4875 
8.250 


NA 


A1 2 3 

FeO 


NA 
NA 


Fe 2 3 

Si0 2 


NA 
NA 

NA 


P 9 0s 


NA 


Ti0 2 


NA 


NiO 


NA 


ZnO 


NA 


d-spacing. . .A. . 
Unit cell. . .A. . 


2.4950 
8.275 




11 


12 


13 


14 


15 


16 


17 


18 


19 


20 


Analysis, wt %: 
MgO 


NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
2.5065 
8.313 


NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
2.5005 
8.293 


11.0 

15.2 

9.3 

7.7 

54.2 

0.16 

0.12 

0.50 

0.12 

0.05 

2.5040 

8.305 


12.3 

11.7 

14.0 

6.3 

52.7 

0.12 

0.19 

0.45 

0.08 

0.10 

2.5005 

8.293 


11.3 

22.9 

15.0 

5.6 

43.1 

0.11 

0.07 

0.53 

0.11 

0.07 

2.4890 

8.255 


11.4 
31.9 
17.0 
13.4 
25.8 
0.30 
0.09 
1.05 
0.13 
0.09 
2.4835 
8.237 


11.7 

8.5 

17.0 

3.5 

53.9 

0.19 

0.07 

0.22 

0.03 

0.47 

2.5045 

8.306 


9.9 
34.6 
12.0 
11.1 
28.2 
0.12 
0.08 
0.48 
0.18 

0.112 
2.4775 

8.217 


8.6 
15.0 
15.0 
14.1 
46.1 
0.17 
0.19 
0.32 
0.17 
0.14 
2.5045 
8.306 


12.9 


FeO 


12.9 

13.0 


Si0 2 


9.2 
49.8 
0.09 


P 9 Or 


0.20 


Ti0 2 


0.45 


NiO 


0.10 


ZnO 


0.06 


d-spacing. . . A. . 
Unit cell. . .A. . 


2.5015 
8.296 




21 


22 


23 


24 


25 


26 


27 


28 


29 


30 


Analysis, wt %: 
MgO 


11.7 

8.5 

4.2 

15.6 

58.2 

0.23 

0.17 

0.39 

0.07 

0.05 

2.4925 

8.267 


11.6 

7.8 

6.8 

9.6 

59.5 

0.39 

0.10 

0.30 

0.12 

0.04 

2.4975 

8.283 


16.4 

16.7 

14.0 

7.4 

43.6 

0.22 

0.12 

0.44 

0.08 

0.10 

2.4990 

8.288 


NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
NA 
2.5000 
8.291 


13.4 

10.1 

9.1 

6.5 

57.4 

0.53 

0.11 

0.31 

0.07 

0.06 

2.4990 

8.288 


8.4 
22.4 
16.0 
15.2 
36.0 
0.64 
0.09 
0.44 
0.08 
0.12 
2.4945 
8.273 


12.0 

9.8 

4.6 

12.3 

56.4 

0.45 

0.09 

0.32 

0.08 

0.06 

2.4960 

8.278 


13.5 

3.6 

14.0 

3.6 

59.8 

0.24 

0.14 

0.03 

0.02 

0.08 

2.5120 

8.331 


NA 

NA 

20.0 

NA 

NA 

NA 

NA 

NA 

NA 

NA 

2.4955 

8.277 


NA 


FeO 


NA 
19.0 


Si0 2 


NA 
NA 
NA 


P 9 Or 


NA 


Ti0 2 


NA 


NiO 


NA 


ZnO 


NA 


d-spacing. . .A. . 
Unit cell. . .A. . 


2.4970 
8.282 



See explanatory notes at end of table. 



11 





31 


32 


33 


34 


35 


36 


37 


38 


39 


40 


Analysis, wt %: 






















MgO 


14.6 


17.7 


NA 


17.5 


10.0 


11.0 


9.1 


6.6 


10.7 


4.5 


A1 2 3 


11.8 


7.2 


NA 


7.6 


8.2 


9.9 


9.1 


7.0 


9.8 


15.5 


FeO 


11.0 


8.5 


10.0 


16.0 


13.0 


16.0 


13.0 


16.0 


22.0 


21.0 


Fe 2 3 


5.8 


7.4 


NA 


1.9 


6.2 


4.5 


7.6 


4.9 


0.0 


9.2 


Cr 2 3 


54.6 


53.6 


NA 


51.6 


58.8 


57.1 


57.8 


59.7 


60.3 


46.9 


Si0 2 


.20 


.28 


NA 


.49 


.01 


.18 


.19 


NA 


.08 


.70 


P2O5 


.08 


.10 


NA 


.11 


.21 


.10 


.07 


.04 


.11 


.08 


Ti0 2 


.44 


.30 


NA 


.29 


.24 


.28 


.29 


.27 


.31 


.38 


NiO 


.09 


.09 


NA 


.09 


.04 


.06 


.07 


.03 


.05 


.03 


ZnO 


.04 


.05 


NA 


.05 


.05 


.05 


.04 


.05 


.04 


.14 


d-spacing. . .A. . 


2.5020 


2.5045 


2.5025 


2.5040 


2.5050 


2.5065 


2.5070 


2.5100 


2.5065 


2.5030 


Unit cell. . .A. . 


8.298 


8.306 


8.300 


8.305 


8.308 


8.313 


8.315 


8.325 


8.313 


8.302 


Sample No 


41 


42 


43 


44 


45 


46 


47 


48 


49 


50 


Analysis, wt %: 






















MgO 


8.7 


NA 


NA 


NA 


15.3 


13.2 


NA 


11.2 


10.3 


NA 


A1 2 3 


10.3 


NA 


NA 


NA 


11.8 


17.6 


NA 


11.3 


18.1 


NA 


FeO 


19.0 


NA 


NA 


NA 


13.0 


13.0 


15.0 


17.0 


18.0 


20.0 


Fe 2 3 


9.6 


NA 


NA 


NA 


5.4 


7.2 


NA 


8.2 


14.0 


NA 


Cr 2 3 


49.2 


NA 


NA 


NA 


51.7 


46.7 


NA 


48.2 


38.1 


NA 


Si0 2 


.46 


NA 


NA 


NA 


.47 


.15 


NA 


.08 


.21 


NA 


p 2 o 5 


.11 


NA 


NA 


NA 


.13 


.12 


NA 


.14 


.14 


NA 


Ti0 2 


.36 


NA 


NA 


NA 


.27 


.25 


NA 


.23 


.75 


NA 


NiO 


.10 


NA 


NA 


NA 


.09 


.08 


NA 


.04 


.09 


NA 


ZnO 


.09 


NA 


NA 


NA 


.05 


.08 


NA 


.10 


.23 


NA 


d-spacing. . .A. . 


2.5120 


2.5155 


2.5255 


2.5260 


2.4995 


2.4915 


2.5090 


2.5045 


2.4985 


2.5005 


Unit cell... A. . 


8.331 


8.343 


8.375 


8.380 


8.290 


8.263 


8.321 


8.306 


8.286 


8.293 


Sample No 


51 


52 


















Analysis, wt %: 








MgO 


15.7 


6.2 


















A1 2 3 


9.4 


8.3 


















FeO 


11.0 


22.0 


















Fe 2 3 


8.7 


12.8 


















Cr 2 3 


49.4 


48.2 


















Si0 2 


.66 


.15 


















P2O5 


.08 


.15 


















Ti0 2 


.22 


.14 


















NiO 


.09 


.03 


















ZnO 


.06 


.38 


















d-spacing. . .A. . 


2.5075 


2.5095 


















Unit cell... A.. 


8.316 


8.323 



















NA Not analyzed. 

'All analyses by X-ray flu- 
orescence except FeO which 
was done by Reno Research 
Center using wet chemical 
methods. X-ray fluorescence 
and X-ray diffraction results 
by Alaska Field Operations 
Center, Juneau, AK. 



12 



APPENDIX B. —NUMBER OF CATIONS PER 32 OXYGENS 





2 


3 


8 


13 


14 


15 


16 


17 


18 


19 


Cation: 

Fe 2 + 


3.70 
4.30 
0.49 
12.00 
3.51 

0.88 

0.46 
0.77 


3.80 
4.20 
1.34 
7.19 
7.47 

0.78 

0.47 
0.49 


4.44 
3.56 
2.55 
5.13 
8.32 

0.80 

0.55 
0.38 


2.57 
5.43 
1.39 
10.30 
4.31 

0.73 

0.32 
0.71 


3.12 
4.88 
1.26 
11.07 
3.67 

1.00 

0.39 
0.75 


3.42 
4.58 
1.03 
8.35 
6.62 

0.90 

0.43 
0.56 


3.65 
4.35 
2.37 
4.79 
8.84 

0.92 

0.45 
0.35 


3.59 
4.41 
0.76 
12.34 
2.90 

1.15 

0.45 
0.81 


3.24 
4.76 
1.87 
4.99 
9.14 

0.69 

0.41 
0.35 


3.96 


Mg 2 + 


4.04 


Fe 3 + 


2.62 


Cr 3 + 


9.00 


Al 3 + 


4.37 


R0/R 2 O 3 2 


0.78 


Molecular ratio: 3 
Cr 3+ /Cr 3+ Al 3+ 


0.49 
0.67 




20 


21 


22 


23 


25 


26 


27 


28 


31 


32 


Cation: 

Fe 2 + 


2.89 
5.11 
1.80 
10.24 
3.96 

0.98 

0.36 
0.72 


1.34 
6.65 
6.65 
3.67 
5.68 

1.48 

0.17 
0.82 


1.98 
6.02 
1.82 
11.86 
2.32 

0.72 

0.25 
0.84 


2.59 
5.41 
1.49 
9.23 
5.27 

1.21 

0.32 

0.64 


2.21 
5.79 
1.26 
11.68 
3.06 

0.89 

0.27 
0.79 


4.13 
3.87 
2.76 
6.87 
6.37 

0.78 

0.52 
0.52 


1.42 
6.58 
2.26 
10.91 
2.83 

0.66 

0.17 
0.79 


2.94 

5.06 

0.80 

13.95 

1.25 

1.17 

0.37 
0.92 


2.38 
5.62 
1.14 
11.24 
3.62 

1.01 

0.30 
0.76 


1.70 


Mg 2 + 


6.30 


Fe 3 + 


1.58 


Cr 3 + 


12.01 


Al 3 + 


2.41 


RO/R 2 3 2 


1.19 


Molecular ratio: 3 
Cr 3+/ Cr 3+ A1 3+ 


0.21 
0.83 




34 


35 


36 


37 


38 


39 


40 


41 


45 


46 


Cation: 

Fe 2 + 


2.71 
5.29 
0.45 
12.75 
2.80 

1.54 

0.34 
0.82 


3.37 
4.63 
1.23 
12.23 
2.54 

0.85 

0.42 
0.83 


3.60 
4.40 
0.90 
12.00 
3.10 

0.99 

0.45 
0.79 


3.56 
4.44 
1.47 
11.76 
2.76 

0.77 

0.33 
0.81 


4.61 
3.39 
1.00 
12.77 
2.23 

0.79 

0.58 
0.85 


4.29 
3.71 

0.00 

12.88 

3.12 

1.16 

0.53 
0.81 


5.79 
2.21 
1.78 
9.53 
4.69 

0.78 

0.72 
0.67 


4.41 
3.59 
1.98 
10.68 
3.33 

0.99 

0.55 
0.76 


2.58 
5.42 
1.10 
11.11 
3.78 

1.14 

0.32 
0.75 


2.85 


Mg 2 + 


5.15 


Fe 3 + 


1.37 


Cr 3 + 


9.36 


Al 3 + 


5.26 


RO/R 2 3 2 


0.97 


Molecular ratio: 3 
Cr 3+ /Cr 3+ Al 3+ 


0.35 
0.64 




48 


49 


51 


52 














Cation: 

Fe 2 + 


3.68 
4.32 
1.71 
10.58 
3.70 

1.07 

0.46 
0.74 


3.96 
4.04 
2.72 
7.77 
5.51 

0.98 

0.50 
0.58 


2.26 
5.74 
1.85 
11.02 
3.13 

1.15 

0.28 
0.78 


5.33 
2.67 
2.68 
10.50 
2.72 

0.96 

0.66 
0.80 




Mg 2 + 




Fe 3 + 




Cr 3+ 




Al 3 + 




RO/R 2 3 2 




Molecular ratio: 3 
Cr 3+ /Cr 3+ Al 3 + 





Stevens (12). Unit cell contains 8 R 2+ cations, 
16 R 3+ cations, and 32 oxygen atoms. 

Ratio based on molecular proportions calcu- 
lated from data in appendix A. 

3 Molecular ratios are calculated from data in 
appendix A and are plotted on figure 5. Fe 2+ / 



Fe 



2 + 



r 2 + 



+ Mg z represent values along the x-axis, 
and Cr 3+ /Cr 3+ + Al 3+ represent values along the 
y-axls. 



13 



APPENDIX C— MINERAL TERMS AND SAMPLE KEY 



Sample 



Field 



Locality 



Mineral terms 



LOCALITIES IN INTERIOR ALASKA 



1 , 

2 , 

3 , 

4 

5 

6 

7 

8 

9 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19.. 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

32 

33 

34 

35 

36 

37 

38 

39 

40 

41 

42 

43 

44 

45 

46 

47 

58 

49 

50 

51 

52 

ND Insuffici 



WB20438. 
WB16537, 
WB16538. 
WB20435. 
WB20436. 
WB20437. 
WB16539. 
WB16540. 
WB16541. 
WB20825. 
WB20826. 
WB20827. 
WB16768. 
PT16641. 
PT16637. 
PB15787. 
PT16635. 
PT16638. 
PT16639. 
PT16636. 
KW20780. 
KW20782. 
KW20779. 
KW19476. 
KW19477. 
KW19868. 
KW19881. 



Avan Hills, 
...do , 



.do, 



. . .do. 
. . .do, 
...dc 



lo, 
. . .do , 
. . .do, 
. . .do, 
...dc 



lo 

. . .do. 

. . .do 

. . .do 

Caribou Mountain. 

. . .do. 

. . .do 

Kanuti River 

. . .do 

. . .do , 

. . .do 

Yuki River 

. . .do 

. . .do. 

Mount Hurst , 

. . .do. 

. . .do 

...do 



ND. 

Magnesiochromite, aluminian. 

Spinel, chromian. 

ND. 

ND. 

ND. 

ND. 

Hercynite, chromian. 

ND. 

ND. 

ND. 

ND. 

Magnesiochromite, aluminian. 

Do. 

Do. 
Spinel, chromian. 
Magnesiochromite, ferroan. 
Spinel, chromian. 
Magnesiochromite, aluminian. 

Do. 
Magnesiochromite, ferrian. 
Magnesiochromite, aluminian. 

Do. 
ND. 

Magnesiochromite, aluminian. 
Chromite, aluminian. 
Magnesiochromite, aluminian. 



LOCALITIES ALONG EXTENSION OF CHUGACH MOUNTAINS 



CM20261. 
CM20268. 
CM19277. 
CM18624. 
CM19649. 
CM11168. 
CM19641. 
CM17679. 
CM19680, 
CM17675. 
CM17670, 
CM17670. 
CM19312. 
CM19322. 
CM19326, 
CM19371. 
CM19373. 
CM20488. 
CM20497. 
CM18678. 
CM20467, 
CM20466, 
CM20443. 
1S153... 
2S430... 



Grant Lagoon 

Halibut Bay 

. . .do 

. . .do 

. . .do 

• . .do. 

Miners Bay 

Claim Point 

. . .do. 

Red Mtd-Kenai 

. . .do 

. . .do. 

Eklutna 

Wolverine Complex. 
...do 



. . .do. 

. . .do ..< 

Tons ina-Bernar d . 

. . .do , 

...do 



Sheep Hill.... 

. . .do 

Dust Mountain. 
Red Bluff Bay. 
. . .do 



Magnesiochromite, ferroan. 

ND. 

ND. 

Magnesiochromite, aluminian. 

Do. 
ND. 
Magnesiochromite, ferroan. 

Do. 

Do. 

Do. 
Chromite, magnesian. 

Do. 

Do. 

Do. 
ND. 
ND. 
ND. 
Magnesiochromite, aluminian. 

Do. 
ND. 
Magnesiochromite, ferroan. 

Do. 
ND. 
Magnesiochromite, aluminian. 

Do. 



ent data to designate mineral term (no chemical data). 



#11. S. GPO: 1985-505-019/20,049 



INT.-BU.OF MINES, PGH., PA. 27971 



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